The invention concerns lubricating compositions having improved properties. Another aspect of the invention relates to additive compositions which impart rust inhibiting properties to lubricating compositions.
Lubricating compositions coming in contact with metal surfaces must possess not only good lubricating properties, but also good anticorrosion and rust inhibiting properties. Various rust inhibitors and corrosion inhibitors are known in the art.
A known rust inhibitor is N-acylsarcosine which is used in the form of metal salt described in U.S. Pat. No. 2,841,555, further in conjunction with a solubilizing alkyl primary amine described in U.S. Pat No. 2,790,779 or together with diamines disclosed in U.S. Pat No. 2,935,389 and ethylene oxide-rosin amine reaction products in U.S. Pat. No. 3,116,252.
Another known rust inhibitor for hydrocarbon oils is dicarboxylic acid disclosed in U.S. Pat No. 2,644,793 which can be reacted with a primary or secondary amine as disclosed in U.S. Pat. No. 2,604,451. Amine salts of polymaleic acid are described in U.S. Pat. No. 4,435,298.
Surprisingly, it has been discovered that N-acylsarcosines produce a synergistic rust inhibiting effect in lubricating greases when combined with a dibasic acid and certain amines in critical proportions.